Constant fuel-air ratio device



Nov. 12, 1957 H. M. FOX

cons'mu'r FUEL-AIR RATIO DEVICE 3 Sheets-Sheet 1 Filed D80. 28, 1953 m 2l 0 Z Mm O MA/ I: 3%

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FIG.

INVENTOR.

7 AT TOR N EYS Nov. 12, 1957 H. M. FOX

consmw FUEL-AIR RATIO DEVICE 3 Sheets-Sheet 2 Filed Dec. 28. 1953RESILIENT MATERIAL I I I l I I I G n0 FIG. 3

METAL ST RIPS INVEVTOR.

' H. M. FOX

ATTORNEYS Nov. 12, 1957 H. M. FOX

consmrr FUEL-AIR 1mm nsvxcza 3 Sheets-Sheet 3 Filed Dec. 28, 1953 ATTORNEYS United States Patent 2,812,932 CONSTANT FUEL-AIR RATIO DEVICEHomer M. Fox, Tuxedo, 0kla., assignor to Phillips Petroleum Company, acorporation of Delaware a device for maintaining a fuel and air mixingdevice. it relates to carburetors This invention relates to constantfuel-air ratio in a In one of its more specific aspects for internalcombustion engines. In another of its more specific aspects, thisinvention relates to a variable-diameter venturi for automaticallymaintaining a constant ratio of mass air fiow with respect to the fuelflow. In still another of its more specific aspects, this inventionrelates to a means for decreasing the linear velocity of air through theventuri of a carburetor as the atmospheric pressure decreases.

Reciprocating internal combustion engines utilizing carburetor devicesfor forming the combustible mixture of fuel vapor and air to be burnedin the cylinders of the engine are usually adjusted with particularatmospheric conditions of air density or temperature and pressure toobtain the development of maximum power and most efficient operation ofthe engin With changes in operating conditions of the engine, such as achange of pressure resulting from a change in altitude, the density ofthe air supplied to the engine is considerably different than when thefuel-air mixing devices of the engine were originally adjusted; andinefficient operation of the engine results. For example, as thealtitude at which the engine is operating is increased, as in mountaindriving, the density of the air decreases so that the mass air flowintroduced into the engine is reduced. Since the fuel metering isusually accomplished on a volume basis, this reduction in mass air flowresults in the formation of excessively rich fuel-air mixtures and areduction in the power developed by the engine.

The present invention provides an adjustable air throat in the venturiof a carburetor and comprises means by which the linear velocity of theair to a reciprocating internal combustion engine is regulated inaccordance with the pressure of the ambient air supplied to the engine.With the variable throat device of this invention, the effective area ofthe inlet air passage of the carburetor is varied by expanding andcontracting the venturi throat of the air passage, in response tochanges in atmospheric pressure, and thereby regulating the linearvelocity of air to the engine. Thus, the apparatus of this inventionprovides improved fuel-air matching for internal combustion enginesoperating under variable conditions of air pressure.

Each of the following objects will be attained by at least one of theaspects of the invention.

It is an object of this invention to provide a device for maintaining asubstantially constant fuel-air ratio regardless of changes inatmospheric pressure.

It is another object to provide a variable-diameter venturi for acarburetor.

It is another object to provide a variable-diameter venturi wherein thediameter is varied in response to the atmospheric pressure.

Another object is to provide an improved carburetor wherein the linearvelocity of air can be maintained constant when the atmospheric pressurevaries.

ice

It is still another object to provide a carburetor having a venturiwhose throat area is controlled by a pressurescnsitive means.

Other objects and advantages will be apparent to one skilled in the artupon study of this disclosure and the accompanying drawing.

Figure 1 is a vertical sectional view of a preferred embodiment of theinvention.

Figure 2 is a view along line 2-2 of Figure 1.

Figure 3 is a vertical sectional view of a modification of the venturiof this invention.

Figure 4 is a vertical sectional view cation of the venturi of thisinvention.

Figure 5 is a plan view of Figure 4.

Figure 6 is a schematic sectional view of a carburetor embodying apreferred form of this invention.

Referring to Figure 1, the air supply to the carburetor comprisesvertical cylindrical tubular casing 10 containing an enlarged centersection 11. Fuel is supplied to the carburetor from float chamber 27 byfuel line 12, the end of line 12 being located in the proximity of thevena contracta of venturi 14 and the flow of the fuel-air mixture to themanifold of the engine being regulated by throttle valve 13 located inthe lower end of air-supply tube 10 and operated by lever 28.

The venturi section comprises variable venturi tube 14 anchored at itsupper end to air duct 10 in truncated annular ledge 15 and rigidlyattached at its lower end to end ring 16 which is movably engaged withair duct 10 through a plurality of pins 17 moving in a like number ofslots 18 located in the inner wall of air tube casing 10. Slots 18comprise a plurality of helical slots in casing 10 so that a verticaland rotating movement is imparted to the attached end of venturi 14 whenring 16 is caused to move. The variable venturi tube is constructed ofcorrugated metal much like a bellows of multiple convolutions whereinthe convolutions are helical so that a vertical and twisting force onthe movable end of the venturi tube results in a change in the effectivecross-sectional area of the throat of the venturi tube. The arrangementof slots 18 in air tube casing 10 is better shown in Figure 2 which is aview of the inner surface of casing 10 taken along line 22 in Figure 1.In Figure 2, it is readily apparent that a downward force on pin 17 inslot 18 causes end ring 16 to be rotated to the right in Figure 2. Anynumber of pins and slots can be employed, depending on the design of theapparatus, and usually at least two such pins and slots are used.

The pressure-sensing device in the apparatus of this invention comprisesan evacuated annular Sylphon bellows 19 located in annular chamber 20formed between the outer surface of variable venturi 14 and the innersurface of section 11 of tubular air casing 10. Annular chamber 20 is inpressure communication with the atmosphere through a plurality of vents21 so that atmospheric pressure is present in chamber 20. Bellows 19 isrigidly attached to air casing 10 at the upper end of annular chamber 20by means of truncated annular ledge 22 so that the lower end of bellows19 can expand or contract vertically in chamber 20. The expansion andcontraction of bellows 19 is transmitted by a plurality of rigid shafts23 attached to the lower end of bellows l9 and operatively engaged withend ring 16 in such a manner that the downward force on end ring 16causes it to rotate through the action of pins 17 in slots 18 to expandand twist venturi tube 14 and thereby increase the effectivecross-sectional area of the throat of venturi tube 14. The movablecontact between the lower end of shafts 23 and end ring 16 is obtainedthrough the use of rollers 24 attached to the ends of shafts 23 by pins25 and arranged to roll along a circumferential path of anothermodifialong the surface of end ring 16. Bellows 19 is spring loaded by acompression-type spring 26 having a spring constant of such a value thatthe smallest elfective crosssectional area of the throat of venturi tube14 is present with sea level pressure conditions.

The operation of my constant fuel-air ratio device, when employed in thecarburetor of an internal combustion engine, is obtained in thefollowing manner. The Sylphon bellows 19 is adjusted so that thesmallest diameter of the throat of variable venturi is at sea levelatmospheric pressure conditions. As the air pressure is reduced byoperation of the internal combustion engine at increased altitudes, forexample, the Sylphon bellows re sponds to the decreased pressure byexpanding and thus imparts a vertical and rotating movement to themovable end of venturi 14. The elongation of the venturi in combinationwith the rotational movement which tends to straighten the helicalconvolutions of the venturi expands the venturi throat and permits thepassage of sufficient additional air to compensate for reduction in airpressure. The process is reversed as the air pressure increases.

As the bellows expand with an increase in altitude the throat of thecarburetor is enlarged, as described above, and the resulting decreasein linear air velocity aspirates less fuel, thereby preventing the usualincrease in fuel-air ratio with altitude and assuring operation atfuel-air ratios closer to stoichiometric. The expansion of thecarburetor throat with altitude is adjusted so that the correspondingdecrease in the linear velocity of air is that required to cause adecrease in fuel flow commensurate with the decrease in mass air flow.The reduction in fuel fiow required can be obtained from the followingtable:

Table Altitude, Feet 1 Approximately stolehiometric.

Alt= air-fuel ratl f/A =luel-alr ratio.

Figure 3 illustrates a modification of the venturi of this inventionwherein the venturi is constructed of a compressible and resilientmaterial instead of corrugated metal. In this modification rubber,resinous material and similar materials can be used.

Figures 4 and 5 illustrate another modification of the venturi of theinvention wherein the venturi is constructed of overlapping flexiblemetal strips maintained under compression so that the throat is expandedor contracted by varying the compression on the metal strips.

Figure 6 is a detail view of the venturi of Figure 1 as applied to adownflow type carburetor. The invention can be applied with equaladvantage to an upflow type carburetor.

The invention is applicable to both automobile engines and reciprocatinginternal combustion engines operating in aircraft.

Although the invention has been described for use in an automotiveengine, it has application in other systems where a constant fuel-airratio is desired.

Numerous modifications of the apparatus of this invention can be devisedwithout parting from the spirit and scope of the invention. For example,a number of small circular bellows can be used in place of annularbellows 19 for sensing the pressure changes corresponding to changes inaltitude of the engine. In addition, rigid shafts 23 transmitting themovement of bellows 19 to end ring 16 can be rigidly attached to endring 16 and the upper ends of shafts 23 in movable contact with thelower end of bellows 19 to permit end ring 16 to be rotated by thedownward force exerted on it. Also, a thin tube a fuel and airthrottling means can be used in place of the plurality of shafts 23 toprovide a more rigid linkage between bellows 19 and end ring 16.

Other reasonable variations and modifications are possible within thescope of the disclosure of this invention, the essence of which is theprovision of a constant fuel-air ratio device comprising a venturi in anair passageway which is expanded and contracted by changes in ambientair pressure.

I claim:

1. In a carburetor for an internal combustion engine comprising an airsupply passage, a fuel supply inlet and a fuel and air throttling meanspositioned in said air supply passage, the improvement comprising asection of said air passage having an enlarged diameter, a helicalcorrugated venturi member positioned within said enlarged section andhaving its upstream end secured in sealing communication with the wallsof said air passage; an annular member secured to the downstream end ofsaid venturi in movable contact with the walls of said air passage; aplurality of helical slots in the inner wall of said air passageadjacent said annular member; a plurality of pin members positionedaround the periphery of said annular member and extending into saidslots; an evacuated cylindrical bellows member positioned in the annularchamber between the venturi member and the walls of the enlarged sectionof said air passage, having one end secured to the upstream end of saidenlarged section and the other end opcratively connected to said annularmember; a compression spring member positioned in said cylindricalbellows member; and means for communicating atmospheric pressure to saidcylindrical bellows member.

2. In a carburetor for an internal combustion engine comprising an airsupply passage, a fuel supply inlet and positioned in said air supplypassage, the improvement comprising a section of said air passage havingan enlarged diameter; a deformable venturi, the diameter of which isdecreased by iongitudinal compression and increased by longitudinaltension, positioned within said. enlarged section and having itsupstream end secured in sealing communication with the walls of said airpassage; an annular member secured to the downstream end of said venturiin movable contact with the walls of said air passage; a plurality ofhelical slots in the inner wall of said air passage adjacent saidannular member; a plurality of pin members positioned around theperiphery of said annular member and extending into said slots; anevacuated cylindrical bellows member positioned in the annular chamberbetween the venturi member and the walls of the enlarged section of saidair passage, having one end secured to the upstream end of said enlargedsection and the other end operatively connected to said annular member;a compression spring member positioned in said cylindrical bellowsmember; and means for communicating atmospheric pressure to saidcylindrical bellows member.

3. In a carburetor for an internal combustion engine comprising an airsupply passage, a fuel supply inlet and a fuel and air throttling meanspositioned in said air supply passage, the improvement comprising asection of said air passage having an enlarged diameter, a flexible,deformable venturi constructed of flexible, coaxially disposed,overlapping metal strips, the diameter of which is decreased bylongitudinal compression and is increased by longitudinal tensionpositioned within said enlarged section and having its upstream endsecured in sealing communication with the walls of said air passage; anannular member secured to the downstream end of said venturi in movablecontact with the walls of said air passage; a plurality of helical slotsin the inner wall of said air passage adjacent said annular member; aplurality of pin members positioned around the periphery of said annularmember and extending into said slots; an evacuated cylindrical bellowsmember positioned in the annular chamber between the venturi member andthe walls of the enlarged section of said air passage, having one endsecured to the upstream end of said enlarged section and the other endoperatively connected to said annular member; a compression springmember positioned in said cylindrical bellows member; and means forcornmunicating atmospheric pressure to said cylindrical bellows member.

4. In a carburetor for an internal combustion engine comprising an airsupply passage, a fuel supply inlet and a fuel and air throttling meanspositioned in said air supply passage, the improvement comprising asection of said air passage having an enlarged diameter, a deformableventuri constructed of rubber the diameter of which is decreased bylongitudinal compression and is increased by longitudinal tensionpositioned within said enlarged section and having its upstream endsecured in sealing communication with the walls of said air passage; anannular member secured to the downstream end of said venturi in movablecontact with the walls of said air passage; a plurality of helical slotsin the inner wall of said air passage adjacent said annular member; aplurality of pin members positioned around the periphery of said annularmember and extending into said slots; an evacuated cylindrical bellowsmember positioned in the annular chamber between the venturi member andthe walls of the enlarged section of said air passage, having one endsecured to the upstream end of said enlarged section and the other endoperatively connected to said annular member; a compression springmember positioned in said cylindrical bellows member; and means forcommunicating atmospheric pressure to said cylindrical bellows member.

5. In a carburetor for an internal combustion engine comprising an airsupply passage, a fuel supply inlet and a fuel and air throttling meanspositioned in said air supply passage, the improvement comprising asection of said air passage having an enlarged diameter; a deformableventuri, the diameter of which is decreased by longitudinal compressionand increased by longitudinal tension, positioned within said enlargedsection and having its upstream end secured in sealing communicationwith the walls of said air passage; an annular member secured to thedownstream end of said venturi and contacting the walls of said airpassage for simultaneous longitudinal and rotational movement; anevacuated cylindrical bellows member positioned in the annular chamberbetween the venturi member and the walls of the enlarged section of saidair passage, having one end secured to the upstream end of said enlargedsection and the other end operatively connected to said annular member;a compression spring member positioned in said cylindrical bellowsmember; and means for communicating atmospheric pressure to saidcylindrical bellows member.

6. The device of claim 5 wherein the deformable venturi is constructedof flexible, helically corrugated metal.

7. The device of claim 5 wherein the deformable venturi is constructedof flexible, axially disposed, overlapping metal strips.

8. The device of claim 5 wherein the deformable venturi is constructedof compressible, resilient material.

References Cited in the file of this patent UNITED STATES PATENTS

